This invention relates generally to systems for guiding vehicles, and more particularly, to a system for avoiding obstacles which are present in a field of operation of a robotic vehicle which is operated either fully automatically or with operator assistance. In addition, this invention relates to systems for operation of robotic vehicles from remote locations.
There is a need for a system which can reliably implement real-time obstacle avoidance for autonomous or semi-autonomous vehicles, such as mobile robots. Semi-autonomous vehicles might include robots which are guided at least in part by a human operator from a remote location, or from the location of the vehicle itself, as would be the case with a powered wheelchair.
With respect to remotely controlled vehicles, the applications are essentially limitless. For example, such robots may be used to perform household functions, hospital work, industrial material transport, hazardous environment tasks, such as maintenance and other operations in nuclear power plants, sentry tasks, and military tasks, such as patrolling and mine field maintenance. Currently available robotic vehicles which are used, for example, in bomb squad work, are operated with the aid of video cameras which permit the operator to view the field of operation of the vehicle. However, such video equipment generally has a limited field of view which prevents the operator from seeing all obstacles which might be impacted by the vehicle, and are essentially useless in smoke-filled or steam-filled environments.
As indicated, there is a need for a vehicle, such as a powered wheelchair, where the operator provides assistance in navigation. Oftentimes, persons who use powered wheelchairs are capable of indicating generally a desired direction of travel, but may not be possessed of sufficient motor control to guide the wheelchair through a fairly cluttered environment. Additionally, such persons may be deficient in coordination sufficient to negotiate turns or to steer around obstacles notwithstanding that there may be sufficient room. Impairment such as spasticity, tremors, weakness, poor vision, etc. either restrict of render impossible a handicapped individual's ability to operate a powered wheelchair. There clearly is a need for an assistive control system which integrates with an operator's control input to improve tracking and provide automatic obstacle avoidance. In the case of a powered wheelchair, the controls would typically utilize joy stick or switch inputs, although head positioning, voice command, or other control schemes are possible. It is also desirable that, in addition to obstacle avoidance, the assistive control scheme provide automatic wall following so as to avoid the need for a handicapped individual to maintain a steady course in a long or narrow corridor. Of course, it is highly desirable to avoid the oscillatory performance which has plagued prior art robotic control systems.
Ideally, an assistive steering control system should follow the general direction prescribed by the operator of the device, such as a wheelchair. However, if the vehicle should encounter an obstacle, the system should autonomously avoid collision with that obstacle while trying to maintain the prescribed course as closely as possible. Once the path has been cleared, the vehicle can resume its motion in the prescribed direction. It is additionally desirable that the integral self-protection mechanism permits steering of the wheelchair or other vehicle at high speeds and in cluttered environments without fear of collisions. Thus, there is a need for a system which performs course corrections during vehicle operation, without requiring the vehicle to be stopped, or to be slowed substantially, while it computes its obstacle-avoiding path.
In addition to obstacle avoidance and wall following, it is highly desirable that an autonomous or assisted navigation system have the capacity to ascertain whether the vehicle can be accommodated through narrow passageways, doorways, and tight spaces, and to negotiate a path through same in response to the general indication of a forward control command. Moreover, it is highly preferred that the system have the capacity to recognize obstacles which are not stationary, or which appear suddenly, such as a person or other vehicle exiting a doorway onto a corridor where the subject vehicle is operating.
As indicated, there has been a continuing effort in the prior art to create a vehicle guidance and obstacle avoidance system which permits maximization of the rate at which the vehicle travels and which does not require the vehicle to stop or slow down significantly upon encountering an obstacle. One prior art approach to this problem involves the building of a map in a computer memory which employs cells which correspond to a predetermined active region in the field of operation of the vehicle. The field of operation is divided into corresponding cells, and in response to ultrasonic scanning, an assumed probability function is computed, which is selected to cover a plurality of the subfields by loading into same respective values which are believed to correspond to the probability that an obstacle is present therein. This prior art approach has a variety of significant drawbacks. First, all of the cells within a predetermined range are incremented simultaneously in response to the computation of the assumed probabilistic function. This carries such a significant computational overhead that the vehicle must be stopped upon encountering an obstacle to complete the computation. However, the deficiencies in this known system are not eliminated entirely by use of a faster computer. More specifically, the underlying assumption of the suitability of a particular probabilistic function may be incorrect for a given operating environment or distribution of obstacles, and may result in the computation of an incorrect function. Succinctly stated, the general characteristics of the distribution of obstacles must be ascertained so as to permit selection of the most likely appropriate probabilistic function to be computed, and which will subsequently result in the incrementation of the cells. The ultimate end to be achieved by this known system is the generation of a map of the probability, or likelihood, of the presence of an obstacle in any given cell. After the map is constructed the vehicle is steered around the obstacles. This approach is so computation intensive that it cannot be implemented without stopping the vehicle. Additionally, the known system is unable to achieve a level of resolution sufficient to permit maneuvering of a vehicle through an obstacle-cluttered environment.
It is, therefore, an object of this invention to provide a simple and economical system for guiding an autonomous vehicle through a field of operation having obstacles thereon.
It is another object of this invention to provide a vehicle guidance system which can effect obstacle avoidance without stopping or slowing the vehicle significantly.
It is also an object of this invention to provide a vehicle guidance system which is responsive to operator input while simultaneously affording protection from collision with obstacles.
It is a further object of this invention to provide a system which can prevent collisions with rapidly appearing obstacles by a vehicle.
It is additionally an object of this invention to provide a system for steering a vehicle from a remote location while the vehicle is in an environment which prevents visual feedback to the operator.
It is yet a further object of this invention to provide a vehicle guidance system which can select automatically between alternative, obstacle-free paths.
It is also another object of this invention to provide a powered wheelchair which can be operated easily by handicapped individuals.
It is yet an additional object of this invention to provide a navigation system having a sufficiently high level of resolution to determine whether a vehicle, such as a motorized wheelchair, can pass through a region of limited width, such as a narrow doorway.
It is still another object of this invention to provide a system for guiding a robotic vehicle in a field of operation having obstacles thereon wherein data from a plurality of sensor types can easily be incorporated into the system.
It is a yet further object of this invention to provide a system for guiding a robotic vehicle in a field of operation having obstacles thereon wherein data from a prior trip by the robotic vehicle obtained from sensors which may be arranged on or off of the robotic vehicle, can be incorporated into a memory and used to help guide the robotic vehicle during subsequent trips.